This invention relates generally to machines and methods for bending blanks of straight rods into U-bolts and, more particularly, a device and method for centering the rod on the U-bolt bending machine prior to bending.
In the manufacture of large steel U-bolts of the type typically used to secure a semi-trailer body to a wheel supported frame or a leaf spring to a wheel supported axle, a long steel cylindrical rod is used. Commonly, the rod has a diameter of between xe2x85x9c inch and 1 xc2xd inches. Threads are then formed or cut onto the opposite ends of the rod. The threaded straight rods are then successively inserted into a hydraulically or power operated bending machine which bends or cold forms each rod around a mandrel to produce a U-shaped bolt.
A properly formed U-bolt has a pair of legs which are of equal length. Otherwise, U-bolts which are formed with one leg longer than the other frequently cannot be used and must be scrapped since the bolts cannot be re-straightened and reformed. Therefore, it is important to accurately position the straight rod in the U-bolt bending machine on the mandrel so that the rod is bent into a U-bolt having equal length legs. One known method of centering or positioning a rod within the bending machine is for an operator to use a tape measure to position the rod so that the mid point of the rod is aligned with the center of the mandrel. This measuring operation requires significant time, it requires the operator to accurately measure and determine the centerline of the rod, mark the centerline and accurately align the rod centerline with the centerline of the mandrel.
Some U-bolt bending machines are equipped with a selectively positioned stop which is fixed at a selected position and used for locating one end of each rod to position the rod properly with its centerline aligned with the centerline of the mandrel. However, when rods of different lengths are successively formed into U-bolts, the position of the end stop must be adjusted according to the length of each rod. Often, the end stop must be frequently adjusted since rods are commonly bent in sets of two or four rods and each set may have a different length. Commonly, a machine operator makes an inaccurate measurement of the length of the rod or an incorrect adjustment of the end stop resulting in a number of straight rods which are formed into U-bolts without equal length legs because the centerline of the rods is not aligned precisely with the centerline of the mandrel on the U-bolt bending machine.
Another prior art approach to centering rods in a U-bolt bending machine is disclosed in U.S. Pat. No. 4,936,131. The invention disclosed in that patent includes permanently marking each rod to indicate the longitudinal center point of the rod. Specifically, the center point of the rod is marked by a stripe of ink directly on the rod or on a label attached to the rod to provide a permanent mark which does not require rotating the rod to find the centerline. The marked centerline is then aligned with a mark located on the center of the machine prior to bending the rod into a U-bolt. However, this system of centering a rod in a U-bolt bending machine has drawbacks. Specifically, the requirement that each rod must be marked or labeled with the centerline. This increases the cost of each rod. Further, a particular operator of a U-bolt bending machine has a limited number of suppliers for rod stock, specifically, those suppliers which offer rods with the centerline indicator thereon.
Moreover, the operator of the U-bolt bending machine still must visually align the centerline of the rod with the centerline of the machine or mandrel for each an every U-bolt being produced. Additionally, to effectively and permanently mark the steel rods, machine oil or other coatings on the steel rod must be effectively removed to apply the tape or marking paint thereto. As such, the rods require additional processing steps and are subsequently more susceptible to corrosion and rust as a result of the removal of these coatings.
Therefore, there is a need for an efficient and effective method and system for centering rods on U-bolt bending machines to consistently produce U-bolts having equal length legs that overcome the above-described shortcomings of known techniques. This invention satisfies these and other objectives while providing a more efficient and economical method of producing U-bolts to substantially reduce the scrap rate of incorrectly formed or bent U-bolts and significantly reducing the bending time. Further, the invention eliminates the need for the supplier, operator or anyone to measure each rod before bending it into a U-bolt, the operator to adjust fixed end stops for various lengths of rod or visually align the centerline mark on the rod with the centerline of the machine.
In a presently preferred embodiment of this invention, a U-bolt bending machine centering device and associated method automatically and accurately positions each rod relative to the mandrel or centerline of the bending machine for accurate, efficient and consistent bending of U-bolts. The centering device is mounted to a standard U-bolt bending machine and includes an elongate carriage fixed to the machine near the mandrel around which the metal rod is bent into a U-shaped bolt. The carriage has a pair of centering plates mounted thereto for conjoint movement in opposite directions toward and away from the mandrel. Each centering plate is coupled to a transport mechanism through a mounting assembly. The transport mechanism in one embodiment includes a pair of elongate rack gears each having a plurality of teeth. The rack gears are contained within slots in the carriage and are vertically spaced one from another. Each rack gear meshes with a pinion gear that is aligned relative to the centerline of the machine or the mandrel around which the rod will be bent.
As a result of the transport mechanism, movement of one centering plane toward or away from the mandrel results in an equal and oppositely directed movement of the other centering plate. Therefore, the straight rod to be formed into a U-bolt can simply be placed on the mandrel in any location between the centering plates. The user manually moves one of the centering plates into contact with the corresponding threaded end of the rod until the opposite end of the rod likewise contacts the opposite centering plate. The movement of the centering plates automatically slides or positions the rod on the mandrel thereby providing a reliable and consistent positioning of the rod in the U-bolt bending machine without the need for marking, measuring or visually aligning the rod.
The mounting assembly for each centering plate includes a pivot pin about which the centering plate can be pivoted downwardly in a direction perpendicular to the orientation of the rod on the mandrel. This provides better access to the carriage or other components of the U-bolt bending machine and avoids interference with the centering plates when they are not needed or in use.